As a perennial night-theme user, (thanks so much for that, staff. It's hugely easier on the eyes) I tend to find the orangey default background a little jarring (no knock on the art, it's quite nice) against the blue-grey backgrounds.

So here's what I propose: while your theme settings are set to "Day", the current default background loads for all lions that do not have a background equipped.

If your theme setting is set to "Night", a nighttime version of the background loads for all lions that do not have a background equipped. (similar to the really beautiful background art that displays around the main content area)

This would be a blanket setting, changing the default background for every lion depending on your theme.